This invention is directed to an apparatus and method for making a parallax stereogram, i.e., free vision stereogram, and particularly for the accurate registration of a plurality of film images in order to ensure stereographic reproduction. The invention is also directed to a projection printing apparatus and method for making a stereogram and enlargements of film images to be used in such stereograms.
A photographic stereogram may be prepared by several methods: (1) a photograph taken with a conventional camera having a single objective and moving it or the object to successive viewpoints; or (2) a photograph taken with a camera having a single objective and an optical stereo attachment which enables two photographs of an object to be taken simultaneously from two viewpoints; or (3) a photograph of an object with a camera having two objectives whose separation is equal to the normal stereoscopic base of approximately 65 mm. A combination of any of the foregoing methods may also be used. Each of the photographs is photographically broken up into a series of narrow strips representing alternatively the picture of the left and right stereogram.
In each of the above techniques the stereoscopic effect is directly related to the accuracy of superimposition of a plurality of images or the optical integration of a plurality of portions of an image. It is therefore seen that the registration of the images for purposes of viewing or printing is of considerable importance.
Furthermore in each of the above methods the single or multiple camera objective are directed to an aim point. The aim point is the point of convergence of the lenses in a multi-objective lens camera or the center of arc of a single lens camera which rotates around the subject or the center of rotation of the subject which rotates during the camera exposure. The aim point is a vertical line within the image that will be at the rear surface of a viewing screen when the finished picture is viewed. The aim point is therefore established and fixed before or when the photosensitive material is exposed. After exposure the aim point cannot be changed or adjusted.
In addition it is often desirable to provide an enlargement of the film image prior to printing. In a conventional photographic apparatus and method the determination of the enlargement occurs simultaneously with the establishment of the air point. In the presently known techniques for making a stereogram the degree of enlargement must be to an exact size to correspond with the pitch of the lens elements of the viewing screen.